As part of an exercise in app building, as well as an exercise in doing useful stuff, I wrote a class browser to inspect the ASP.NET AJAX client libraries. It's a simple ASP.NET-based app, though most of the code is client-side. I wrote a simple reflection layer (inspired in part by the .NET Reflection classes) and then a UI layer that uses it. It's about 1,000 lines of JavaScript and no managed code at all.